DescriptionThe spinner dolphin is a small cetaceans with a slim
build. Adults are typically 129–235 cm and reach a body mass of 23–79 kg. This
species has an elongated rostrum and a triangular or sub-triangular dorsal fin.
Spinner dolphins generally have tripartite colour patterns. The dorsal area is
dark gray, the sides light gray, and the underside pale gray or white. There is
also a dark band that runs from the eye to the flipper, bordered above by a thin
light line. However, the spinner dolphin has more geographic variation in form
and coloration than other cetaceans. In the open waters of eastern Pacific,
dolphins have relatively small skulls with short rostra. There is also a dwarf
form of spinner dolphin that occurs around southeast Asia. In these same
subspecies, a dark dorsal cape dims their tripartite colour patterns. Further
offshore, subspecies tend to have a paler and less far-reaching cape. In certain
subspecies, some males may have upright fins that slant forward. Some
populations of spinner dolphin found in the eastern Pacific have bizarre
backwards facing dorsal fins, and males with strange humps and upturned caudal
flukes.

Ecology
The spinner dolphin lives in nearly all tropical and subtropical waters between
40°N and 40°S. The species is primarily inhabit inshore waters, islands or
banks. However, in the eastern tropical Pacific, dolphins live far from shore.
Spinner dolphin may use different habitats depending on the season.

The spinner dolphin feed mainly on small mesopelagic fish, squids and sergestid
shrimps and will dive 200-300m to feed on them. Spinner dolphins of Hawaii are
nocturnal feeder and forage in deep scattering layers, which contain many
species. The dwarf spinner dolphin may eat mostly on benthic fish in reefs and
shallow water. Off Oahu, Hawaii, spinner dolphins foraging at night and
cooperatively herd their prey in highly dense patches. They swim around circle
of prey and a pair may swim through it to make a catch. Spinner dolphins are
themselves preyed on by sharks. Other possible predators include then killer
whale, the false killer whale, the pygmy killer whale and the short finned pilot
whale. They are also susceptible to parasites, both external ones like barnacles
and remoras, and internal ones like nematodes, trematodes, cestodes and
acanthocephalans. Spinner dolphins move about the oceans in schools; groups that
vary in size from just a few dolphins to over a thousand. They commonly school
with other species such as Pantropical spotted dolphins, or small toothed
whales. In such schools, spinner dolphins are known to undertake migrations,
following prey or warm water currents. In Hawaii, spinner dolphins usually spend
their days resting in shallow bays near deep water, and then move offshore at
dusk and feed as they move substantial distances along the shore (8). Pelagic
spinner dolphins feed primarily on small mesopelagic fish, squids and shrimps,
and dive down to depths of 300 meters to catch their prey . The dwarf spinner
dolphin feeds on reef fishes and other benthic organisms.

Mating in spinner dolphins appears to be promiscuous, and like many small
dolphins, true courtship behaviour can be observed, such as mutual caressing
between the male and female. The breeding system may vary geographically, with
some populations showing a greater degree of polygyny than others . Calves are
born every three years, after a gestation period of about ten months. The mother
nurses the calf for up to two years, and they form a bond that lasts a lifetime.
Females reach sexual maturity between four and seven years, whereas males do not
reach maturity until between seven and ten years.

The purpose of the energetic spinning behaviour of the spinner dolphin is not
known. It has been suggested that the large cloud of bubbles created by the
powerful spin and splash landing may act as an echolocation target, to allow a
widely dispersed school of dolphins to communicate. Another theory is that the
spinning may dislodge hitch-hiking remoras, or the spinning may, at times,
simply be play.

Behavior and life history
In certain regions, such as Hawaii and northern Brazil, dolphins spend the
daytime resting in shallow bays near deep water. At dusk, they travel offshore
to feed. They travel along the shore during foraging trips, and the individuals
that occupy the same bay may change daily. Some individual dolphin do not
anyways go to a Bay to rest. However, in Hawaii, dolphins do seem to
return to the same site each trip.
Spinner dolphins live in an open and loose social organization. The spinner
dolphins of Hawaii live in family groups but also have associations with others
beyond their groups. Mothers and calves form strong social bonds. Spinner
dolphins seem to have a promiscuous mating system, with individuals changing
partners for up to some weeks. A dozen adult males may gather into coalitions.
Vocalizations of spinner dolphins include whistles, which may be used to
organization the structure of the school; burst-pulse signals, which may serve
to be evocative and vocative and echolocation clicks. The spinner dolphin has a
10 months gestation period, and mothers nurse their young for 1–2 years. Females
are sexuality mature at 4–7 years, with 3 year calving intervals, while males
are sexually mature by 7–10 years. Breeding is seasonal, more so in certain
regions than others.

Spinning behavior
Spinner dolphins are well known for their acrobatics and aerial behaviours. A
spinner dolphin comes out of the water, front first, and twists its body as
ascends in the air. After it reaches its maximum height the dolphin descends
back into the water, landing on its side. A dolphin can make 2-5.5 spins in one
leap. The swimming and rotational speed of the dolphin spinning underwater
affects the number of spins it can do while airborne. These spins may serve
multiple functions. Dolphins may also make nose-outs, tail slaps, flips, head
slap, "salmon leaps" and side and back slaps.

Threats
Spinner dolphins in the eastern tropical Pacific have been killed incidentally
since the early 1960s by tuna purse seine fisheries. They were caught in such
large numbers that the population of S. l. orientalis was reduced to less
than one third of its original size. Following raised awareness of the number of
dolphins killed in tuna purse seine fisheries, measures were implemented to
reduce dolphin by-catch. Today spinner dolphins continue to be killed in this
way, although in greatly reduced numbers. However, continued chase, capture and
release of large numbers in the fishery may be preventing the population from
recovering .

In Sri Lanka and the Philippines, large numbers of spinner dolphins have also
been captured in gillnets and killed by harpoons for the past 20 years, and
local harpoon fisheries exist in several more locations throughout the world.
Incidentally captured dolphins are consumed by local people, or used as shark
bait, and this has led to the development of markets and fisheries directed at
dolphins. The takes in these fisheries may be unsustainable.

Conservation
The eastern tropical Pacific and Southeast Asian populations of the spinner
dolphin are listed on Appendix II of the Convention on Migratory Species (CMS).
This means that the spinner dolphin is a migratory species that needs, or would
significantly benefit from international co-operation, and the convention
encourages the range states to conclude global or regional agreements. The
spinner dolphin is also listed on Appendix II of the Convention on International
Trade in Endangered Species (CITES), meaning that international trade in this
species should be carefully regulated. The value of dolphins as a tourist
attraction offers countries and communities an incentive to protect these
beautiful animals. Fernando de Noronha National Marine Park; (an archipelago off
equatorial Brazil) was established in 1988, to provide nominal protection to
spinner dolphins and support dolphin watching tourism, and it has been reported
that in Zanzibar, the value of spinner dolphins for tourism far exceeded that of
using them as bait for sharks (8). It is hoped that with meaningful laws, the
will and resources to enforce them, continued attention by non-governmental
organizations and efforts to make the public aware of the intrinsic value of
their endemic dolphins, this charismatic species will continue spinning in our
oceans forever.